1. Field of the Invention
The present invention relates generally to the field of pressurized fluid injectors and, for example, more particularly to intensified pressure fuel injectors.
2. Prior Art
Intensified fuel injectors are well known in the prior art. While not so limited, intensified fuel injectors are commonly used as fuel injectors on diesel-cycle internal combustion engines. Prior art patents on such fuel injectors include U.S. Pat. No. 5,460,329 issued to Oded E. Sturman on Oct. 24, 1995 and U.S. Pat. No. 6,257,499 B1 issued to Oded E. Sturman on Jul. 10, 2001. Such fuel injectors have some form of valve and valve control system for controllably providing an actuating fluid, typically fuel or engine oil, to a relatively large piston that mechanically drives a relatively smaller piston to actually pressurize the fuel to a desired higher level for injection purposes. Typically the fluid driving the larger piston is provided from a supply or common rail at a relatively low pressure, with the pressure of the fuel being injected at a higher pressure being a function of the rail pressure and the ratio of the two effective piston areas. The ratio of the areas may be, by way of example, on the order of 9 to 1 so that the pressure of the fuel being injected is much higher than the rail pressure.
If the rail pressure is constant, the rate of fuel injection will be substantially constant. Consequently, the only control over the amount of fuel injected in any single injection event would be the control of the length of time of the injection. This is far less than ideal, particularly under partial load conditions, as it tends to concentrate the injection over too small of a crankshaft angle, and in compression ignition engines, may require concentrating the injection closer to top dead center of the engine cycle than desired.
To help reduce this problem, it is known to vary the rail pressure with engine operating conditions to provide some control over the fuel injection rate, in addition to the control provided by control of the injection duration. However, wide, rapid, and repeatable variation in rail pressures is not an easy thing to accomplish and accordingly, the range of rail pressure variation typically is somewhat limited.